To reduce discharge of fuel vapors into the atmosphere, motor vehicles induct fuel vapors from a fuel tank into the engine. A carbon canister is also coupled to the fuel tank to adsorb fuel vapors under some conditions when the internal combustion engine is not running. The carbon canister, however, has limited capacity.
In the case of plug in hybrid vehicles, the internal combustion engine may not operate for a prolonged period of time. In such systems, the fuel tank may be sealed and at a relatively high pressure. An automatic lock of the fuel cap is provided. Before refueling, the operator presses a dashboard button and, in response, the fuel tank is vented through the carbon canister to reduce fuel tank pressure. When a fuel tank pressure sensor indicates that the fuel tank pressure has fallen to a predetermined level, the fuel cap unlocked.
The inventors herein have recognized an issue with the above type of systems. In the event of a degraded fuel tank pressure sensor, unlocking of the fuel cap may be delayed or impaired. The inventors herein have addressed this issue by venting a fuel tank into a vapor absorbent canister in response to a request to refuel; and unlocking the fuel cap in response to a predetermined temperature change in the canister. As vapors are absorbed in the canister, the temperature rises, and as fuel tank pressure decreases fewer vapors are absorbed, and the canister temperature then declines. These changes in temperature may be used to detect when the fuel tank has depressurized. Such detection may occur in the absence of a fuel tank pressure sensor, or when a fuel tank pressure sensor has degraded. In another aspect of the solution, the detection may also occur in response to both a pressure sensor and detection of a predetermined temperature change.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.